The invention relates to a semiconductor die assembly encapsulation mold and to a method of forming an encapsulation mold.
Multiple semiconductor dies are often encapsulated together in a single encapsulation mold. Multiple semiconductor dies are secured to a single semiconductor die support structure to form a multiple semiconductor die assembly. The dies are then electrically connected, usually by bondwires, to bond pads of the support structure. The assembly is then placed in an encapsulation mold with a first and a second section that join to form a mold cavity. An encapsulation material is inserted into the mold cavity covering the assembly. The assembly is removed from the mold and the assembly is separated or cut, usually by saw cutting, into individual molded semiconductor dies by cutting through the encapsulation material and the support structure.
FIG. 1 is a top view of a conventional multiple semiconductor die assembly 100 after encapsulation and before the semiconductor dies 30 are separated into individual dies 30 along dashed lines 50. FIG. 2 is a cross-sectional view of FIG. 1 taken at line IIxe2x80x94II. The dies 30 are shown secured to the top surface 22 of a semiconductor die support structure 20 such as, for example, a thin printed circuit film or board. There are many well known techniques for securing the dies 30 to the support structure 20, such as die paste. FIGS. 1 and 2 illustrate an assembly 100 of six dies 30 mounted on a single support structure 20. After the semiconductor dies 30 are mounted various electrical connections 31, such as wire bonds, are made between the dies 30 and the support structure 20. The dies 30 and the support structure top surface 22 are covered with an encapsulation material to form an encapsulation layer 40 which has a top surface 42 and sidewalls 43 supported by the support structure""s top surface 22. The encapsulation layer can be formed by using an encapsulation mold as described in FIG. 3.
FIG. 3 illustrates a conventional encapsulation mold 200 for forming the encapsulated assembly 100 of FIGS. 1 and 2. The dies 30 secured on a support structure 20 are placed inside the encapsulation mold 200. A conventional encapsulation mold 200 consists of two sections, a base section 60 and a top section 61. The base section 60 and top section 61 are secured to each other along a shared perimeter 63 by various means well know in the art. The two sections 60, 61, when secured, form a mold cavity 64. The mold 200 contains an aperture 62 for transferring encapsulation material into the mold cavity 64. The base section 60 is shown secured against the support structure""s bottom surface 21 so that the encapsulation material does not extend past the perimeter 23 of the support structure 20. The encapsulating material is conventionally injected through the aperture 62 under pressure until the mold cavil 64 is filed. Conventional encapsulating material 40 include various plastics and resins such as various molded epoxy compounds.
After the encapsulation layer 40 is formed, the mold 200 is removed. Various electrical contacts, such as fine ball grid arrays 36 (FIG. 2) formed on the support structure""s bottom surface 24, can be formed on the assembly 100 after encapsulation. Dashed lines 50 of FIGS. 1 and 2 outline the regions where the assembly is cut or singularized into individual packaged dies 30. A conventional method is to saw cut the assemble 100 along the dashed lines 50, with the saw entering the assembly 100 from the encapsulation layer""s top surface 42. However one drawback of conventional assembly 100 is that the encapsulating layer 40 often crumples, chips or is otherwise damaged in the separation region 50 during the separation or cutting phase. Uneven or non-uniform surfaces can be created as a result of the separation process.
Another drawback is that the encapsulating layer 40 quickly dulls the cutting blade, so that a thick encapsulation layer 40 slows the singulation process. A third drawback of the conventional method is that the encapsulating layer 40 typically has a different coefficient of thermal expansion than the support structure 20 which may cause the support structure""s perimeter 23 to curl up or bow toward the encapsulation layer""s top surface 42. If the support structure 40 bows, it can make the assembly 100 separation process very difficult and result in non-uniform individual die packages 30. The bowing can also interfere with various electrical contacts formed on the assembly 100 after encapsulation, such as the fine ball grid array 36 shown in FIG. 2.
Accordingly, it is desirable to provide an encapsulation mold and a method of encapsulating semiconductor assemblies which makes it easier to separate the molded assembly into uniformly shaped individual packaged dies and which reduces the tendency of the assembly""s support structure to bow upwards. It is also desirable to improve the uniformity among separated packaged semiconductor dies, reduce the cost and complexity of fabricating packaged semiconductor dies, and reduce damage to the encapsulation layer during die separation.
The invention addresses some of the drawbacks of conventional semiconductor assembly encapsulation molds as well as problems associated with the encapsulation layer during die separation. A semiconductor assembly including multiple semiconductor dies secured to a single semiconductor support structure are inserted into an encapsulation mold comprising a first mold section and a second mold section. The two sections when secured together form a mold cavity. The second mold section has a design feature which provides an exterior surface molded feature in the molded assembly which facilitates cutting of the encapsulation layer during singulation of the packaged dies. The design feature may be an interconnected continuous groove or interconnected raised rib provided along the interior surface of the mold cavity at die singulation locations.
An encapsulation layer is formed for the assembly using the encapsulation mold with the design feature. Encapsulating material is transferred into the mold until the mold cavity is filled. The encapsulation layer""s exterior surface is shaped according to the design feature of the mold. The semiconductor assembly is then removed from the mold and the individual dies are separated from each other by cutting the encapsulation layer and support structure along lines of the encapsulation layer""s exterior surface design feature shaped by the interior design feature of the mold.
In one exemplary embodiment, the mold""s design feature is a interconnected cavity formed on the interior surface of the mold and projecting out from the main mold cavity. The resulting encapsulation layer""s exterior surface has an interconnected raised ribbed along the separation regions of the dies. In another exemplary embodiment, an encapsulation mold has an interior surface of a interconnected projecting rib design feature projecting into the mold cavity. The resulting encapsulation layer""s exterior surface has an interconnected grove or cavity along the separation regions of the dies.
These and other advantages and features of the invention will be more clearly understood from the following detailed description of the invention which is provided in connection with the accompanying drawings.